In the past sand control methods have been dominated by gravel packing outside of downhole screens. The idea was to fill the annular space outside the screen with sand to prevent the production of undesirable solids from the formation. More recently, with the advent of tubular expansion technology, it was thought that the need for gravel packing could be eliminated if a screen or screens could be expanded in place to eliminate the surrounding annular space that had heretofore been packed with sand. Problems arose with the screen expansion technique as a replacement for gravel packing because of wellbore shape irregularities. A fixed swage would expand a screen a fixed amount. The problems were that a washout in the wellbore would still leave a large annular space outside the screen. Conversely, a tight spot in the wellbore could create the risk of sticking the fixed swage.
One improvement of the fixed swage technique was to use various forms of flexible swages. In theory these flexible swages were compliant so that in a tight spot they would flex inwardly and reduce the chance of sticking the swage. On the other hand, if there was a void area, the same problem persisted in that the flexible swage had a finite outer dimension to which it would expand the screen. Therefore, the use of flexible swages still left the problem of annular gaps outside the screen with a resulting undesired production of solids when the well was put on production from that zone.
Prior designs of screens have used pre-compressed mat held by a metal sheath that is then subjected to a chemical attack when placed in the desired location downhole. The mat is then allowed to expand from its pre-compressed state. The screen is not expanded. This design is described in U.S. Pat. Nos. 2,981,332 and 2,981,333. U.S. Pat. No. 5,667,011 shows a fixed swage expanding a slotted liner downhole. U.S. Pat. Nos. 5,901,789 and 6,012,522 show well screens being expanded. U.S. Pat. No. 6,253,850 shows a technique of inserting one solid liner in another already expanded slotted liner to blank it off and the used of rubber or epoxies to seal between the liners. U.S. Pat. No. 6,263,966 shows a screen with longitudinal pleats being expanded downhole. U.S. Pat. No. 5,833,001 shows rubber cured in place to make a patch after being expanded with an inflatable. Finally, U.S. Pat. No. 4,262,744 is of general interest as a technique for making screens using molds.
U.S. Pat. No. 7,318,481 addresses this issue by providing a screen assembly with an outer layer that can conform to the borehole shape upon expansion. The material is selected that will swell in contact with wellbore fluids to further promote filling the void areas in the borehole after expansion. In an alternative design, screen expansion is not required and the outermost layer swells to conform to the borehole shape from contact with well fluids or other fluids introduced into the wellbore. The screen section is fabricated in a manner that reduces or eliminates welds. Welds are placed under severe loading in an expansion process, so minimizing or eliminating welds provides for more reliable screen operation after expansion.
However, the outer layer that is the screen as described is U.S. Pat. No. 7,318,481 has to make the trip into the borehole and retain its relative position to the base pipe openings that are initially under it. When placed at the desired location it still needs some longitudinal fixation to hold proper positioning relative to the base pipe below. Since such screen materials are heat sensitive, welding retainers is not suitable for this application. What is needed is a fixation device that can be quickly mounted and mechanically anchored to properly place and hold the sleeves that comprise the screen sections that are slipped over the base pipe in the assembly process. On many occasions these assemblies are field assembled so that the components need to be simply constructed so that they can be mounted with available tools at a borehole site or a district distribution location.
In other unrelated applications to swelling packers that hold large differential pressures end retaining devices for the swelling elements that seal a borehole have been used as an integral component of the sealing assembly for protection against end extrusion under high differential pressures. A few examples of such packers are U.S. Pat. Nos. 7,013,979; 7,552,767; 7,441,596 and 7,387,158. Other annularly shaped retainers for fitment on tubulars are made by Downhole Products Ltd. of Edinburgh Scotland and illustrated on their web site with a variety guide shoes and centralizers at http://www.downhole.org/products.html.
What is needed and provided by the present invention is a rapidly deployed over the tubular retainer to properly position porous sleeves used in conjunction with base pipes having openings to retain the sleeves in the desired position for the trip downhole and in service when flow through the sleeve begins. The sleeve is initially retained for the trip into the borehole and continues to be retained after it is in position and has swelled or otherwise grown to span the annular space around the base pipe to the borehole wall. Exterior flats or ridges are provided for rapid assembly using hand tools to allow for field assembly of a screen system. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred and alternative embodiments and the associated drawings while understanding that the full scope of the invention is determined by the appended claims.